Selfish mining is a practice where a miner withholds a block to gain an advantage, creating inefficiencies and waste in the Bitcoin network. While it could benefit some miners, it could lead to centralization and threaten the decentralization of Bitcoin. However, it is not in the best interest of all parties to engage in this behavior.
The financial structure of Bitcoin relies on incentives to encourage honest participation in the network. In a decentralized system, it is crucial to align the interests of all participants to ensure the long-term stability of the network. Financial incentives drive nodes to secure the network. If they act honestly, they stand to be rewarded, but cheating could mean losing potential revenue.
One area where this is especially true is in mining. Large amounts of capital are invested in electricity and specialized hardware, with miners seeking to maximize their returns. The easiest way to do so is by playing by the rules since miners who append a block to the chain receive all of the fees paid on the transactions from their block, as well as a portion of newly-minted coins. This reward is called the block reward and is halved every 210,000 blocks, roughly every four years. At present, the reward is 6.25 BTC but will be reduced to 3.125 after the next halving.
The high financial incentives for mining have led to intense competition, boosting the security and decentralization of the network. However, there are concerns that these incentives could be manipulated.
How Does Selfish Mining Work?
Ittay Eyal and Emin Gun Sirer's 2013 paper "Majority is not Enough: Bitcoin Mining is Vulnerable" offers the most comprehensive explanation of selfish mining, which can lead to the centralization of the network, contrary to popular belief.
Here's how selfish mining works: Suppose the total hash rate is divided equally among four miners, Angela, Roman, Emily, and Alex, each with 25% of the hash rate. While Angela, Roman, and Emily follow the rules, Alex aims to exploit the system for his benefit. Normally, the miner who finds a block adds it to the chain immediately. Angela, Roman, and Emily do so, but if Alex finds a block, he withholds it from the chain, hoping to find another block before anyone else.
Suppose 100,000 blocks have been mined, and the participants are now trying to propose block 100,001. Alex, who already has 100,001 and 100,002 blocks on his secret chain, is now two blocks ahead. As long as he continues to find blocks before the others catch up, he keeps adding blocks to his secret chain.
When the other participants catch up and are one block behind, Alex unveils his longer chain. According to the longest chain rule, the correct chain to follow is the one with the most accumulated Proof-of-Work. So, the other participants will switch to Alex's chain, and any rewards they would have earned on the other chain will no longer exist. Since Alex mined the blocks on the current chain, he keeps all the rewards.
Is Selfish Mining a Threat to Bitcoin?
Selfish mining, a practice where a miner withholds a block to gain an advantage, creates inefficiencies and waste in the Bitcoin network. However, participants who engage in this practice maintain a strategic edge over other participants. Over time, it may cause mining pools to grow in hash rate as other miners team up with selfish entities to maximize revenue. If a single pool acquires the majority of the power, it may try a 51% attack.
Despite these risks, some believe that the Bitcoin network will remain decentralized due to ideological considerations and incentives that motivate miners to keep the ecosystem functioning properly. If the network were to become corrupted, miners would be unable to recover their investments in machinery and electricity or to turn a profit.
Although selfish mining could benefit some miners by increasing their revenue, it could lead to more participants joining the selfish miners and threatening the decentralization of Bitcoin. However, it is not in the best interest of all parties to engage in this behavior. Undermining the network's security could lead to a drop in the Bitcoin price, which would negatively affect the profitability of all mining operations.